Earthquake Prone Area Development

Are you looking at fixing earthquake damaged buildings or constructing in an earthquake prone area?

Following the Christchurch Earthquake sequence, the building requirements in earthquake prone areas has been updated. Whether it be repair of an existing building or a new build, site specific geotechnical assessments are now a routine requirement at Building Consent stage. Geotechnical assessments are used to determine the best type of foundation for your property to mitigate against potential liquefaction risks. KGA can undertake geotechnical assessments of properties in earthquake prone areas for the purpose of rebuilding/repair assessments and for new development.

What Foundation Technical Category (TC) is my property?

Residential properties in the CERA Green Zone on level ground have been assigned on an area wide basis one of three foundation technical categories (TC1, TC2 and TC3) that reflect both the liquefaction experienced to date and future expected performance. These technical categories are intended to guide foundation design and are a starting point for assessing a particular site, in order to determine the appropriate foundation solution for each site. A property’s technical category does not automatically determine the foundation options or actual future performance for that property during an earthquake and site specific geotechnical assessments may lead to different outcomes than indicated by the property’s technical category. Land that is unclassified by EQC will be assessed on a case by case basis.

KGA will review the EQC TC mapping of your property in order to design a site-specific subsurface investigation.  Based on the results of our investigation and analyses, we will determine if the area-wide technical categorisation correlates with the specific ground conditions of your property. It is possible that less (or more) significant foundations will be required for your specific site. KGA will provide foundation solution recommendations tailored to your design plans and the unique ground conditions of your property.

 

Why do I need a geotechnical report?

A geotechnical report is required to determine the most suitable foundation for your structure and is necessary when filing for Building Consent. TC1 and TC2 properties generally require shallow soil testing only to determine the suitability and bearing capacity of the near-surface soils. TC3 properties require deep soil testing, or a review of nearby deep soil tests, to further identify the on site liquefaction hazard.

 

Do I need a repair or a rebuild?

To repair or rebuild is based on many factors and requires a structural assessment and input from a structural engineer. Following a structural assessment, a geotechnical investigation and report will be required to determine how to implement a repair strategy or how to design foundations for a full rebuild. If a structural assessment has not been undertaken, KGA can provide a geotechnical report to cover both repair and rebuild options. KGA works closely with several structural engineering companies and can recommend a company to suit your needs.

 

What does an investigation involve?

The scope of geotechnical investigation required undertaken will be based on the mapped Technical Category of your site. TC1 and TC2 sites require only shallow investigation via hand auger drilling. TC3 sites require deeper soil testing and Cone Penetrometer Probes (CPTs) are used to gather ground data or use in liquefaction assessments.  

The testing is undertaken in such a way as to minimise its impact on your property. Following completion of the testing, the holes are backfilled and the area reinstated.

Following the soil testing, the information is used to provide options for foundation design and is suitable for Resource and Building Consent submissions.

 

Geotechnical testing and/or reporting has already been constructed on my property. Is further investigation necessary?

Updates to the MBIE Guidance document were implemented in 2014. Geotechnical reports dated prior to the updates will need to be reviewed and revised to comply with current industry standards. In many instances, KGA is able to use existing data from previous investigations for the updated analyses and protocols. In rare instances, additional testing is required to meet MBIE requirements.

 

How much does it cost?

Many factors influence the scope of a geotechnical investigations for earthquake prone areas such as location, mapped Technical Category, existing investigation information, type of building to be constructed and land area. Call us on 03 343 5302 to speak to one of the engineers about your project, and they will provide an estimate of the work required.

 

What is a Producer Statement?

Producer statements confirm that aspects of the building design are in compliance with the Building Code or that construction elements have been completed in accordance with an approved Building Consent.

PS1 - confirms that the proposed design will comply with the Building Code

PS2 - confirms that an existing third party PS1 does comply with the Building Code

PS4 - confirms that the building work has been completed in accordance with the Consented plans.

KGA is able to provide you with the relevant Producer Statement for your project.

 

For more details on how we can help you when building in an Earthquake Prone Area, have a look at the following services

Subsurface Investigation | Ground Improvement | Foundation Design | Construction Monitoring